Carrier current transmission system



Feb. 29, 1944. M. J. BROWN 2,3 7

CARRIER CURRENT TRANSMISSION SYSTEM Filed July 11, 1942 3 521 V s 5 super! 290: $523k? 435512?? C'0nf/Jdm'f Fawn-filer f Want-M177?! Mnsmi/fa 8 6 ecs/Per 15/ m 6 Receiver 1 Reqeiver 72/60 5 O g I) i 7 My M5 L5 v T t2 4 WITNESSES: a INVENTOR Myra/7 :ZBrowrr. 72a) w BY Patented Feb. 29, 1944 117" CARRIER CURRENT TRANSMISSION SYSTEM Myron J. Brown, Forest Hills, Pa., assignor to Westinghouse Electric-4t Manufacturing Company, East Pittsburgh, Pa; a corporation of Pennsylvania.

Application July 11, 1942, Serial No. 450,513 2 Claims-.- Jill. 177-353) My invention relates to carrier currenttransmission systems and, in particular, to such systems in which code signals are transmitted over line Wires between a plurality of stations, such as, for example, for supervisory control of an electric power system.

One object of my invention is to provide circuit arrangements which shall insure that the operation of a transmitter at one station shall not interfere with or otherwise affect the operation 110 of a transmitter at a second station.

Another object of my invention is to provide circuit arrangements for the transmitter and receiver at each station which shall be' extremely simple and of low cost and which shall still insure that the operation of the transmitter at one 'station does not interfere in any undesirable way with the operation of the carrier current apparatus at any of the other stations.

Still another object of my invention is to provide a transmitter and receiver for a high-frequency communication system incorporating a band-pass filter of such a type as to insure stability and constancy of transmission to the desired band of waves in spite of variations in the '25 energy being transmitted, and opaqueness to frequency outside that band.

Still another object of my invention is to provide a combined transmitter and receiver circuit for a communication system which shall incor- '30 porate a band-pass filter which is transparent to a particular band of frequencies, and is opaque to the harmonics thereof.

Still another object of my invention is to pr vide a combined receiver and transmitter for a communication system in which tuning'elements are so incorporated as to produce an unusually pure sine wave generation.

Other objects of my invention will'become apparent upon reading the following description "40 taken in connection with the drawing, in which:

Figure 1 is a one-line schematic diagram of a carrier current supervisory control telephone line embodying the principles of my invention;

Fig. 2 is a schematic diagram of the combined transmitter-receiver circuit to be incorporated in each station; and

Fig. .3 is a graph used in explanation of my invention.

Referring to the drawing, Fig. 1 shows a line I, which may, for example, be an ordinary'telephone line, having distributed at various points of its length stations 2, 3 and 4. Each of these stations comprises a transformer 5 interconnecting the local apparatus with the line i a combined transmitter and receiver} embodying circuits shown in more detail in Fig. 2; a supervisory control element 1 by which code signals passing through the transmitter-receiver 6 actuate electrical control devices'for a power station or sub-station; and, if desired, an ordinary telephone 8 which transmits signals through the transform: er 5 and over the line I. To illustrate a typical supervisory control arrangement of the type designated by the numeral 1, reference is made to Patent No. 2,276,646 to H. P. Boswau, issued March 17, 1942, and assignedto Westinghouse Electric & Manufacturing Company, of East Pittsburgh, Pennsylvania. I

In a system of the type illustratedin Fig. l, the transmitter-receiver '6 is provided with arrangements shown in more detail in Fig. '2, by which an operator at one station may send out carrier currents over' the telephone line I which are m'odulated in accordance with any desired code of signals. Thus, by employing a proper code, a signal peculiar to" any one of the other stations connected to the line can be made to operate switching arrangements at that particular station to connect a receiver'which will demodulate the coded signal and actuate any desired circuit controllers for'electrical apparatus located at that particular station in accordance with the subsequent code signals transmitted from the first-mentioned station. Since the details of the code signals and the supervisory control apparatus l responsive thereto form no part of this invention, it is believed to be superfluous to describe them in detail here.

Where the telephoned is provided, the operator may transmit telephone messages over the lin I to an operator at any'of the other stations connected thereto. Since such arrangements "are well known and form no part'of the .present invention, they will not .be further described herein.

It will be evident from the foregoing general description that at each'of'the stations 2, 3 and 4, there must be provided a transmitter for code signals which can be. connected to the circuit when desired, and there must alsobe provided a receiver which shall demo'dulate signals when the transmitter at the station inquestion is not operating. Fig. 2 shows the arrangement which I prefer for the circuits at the 'combinedreceivertransmitter'station and'constitutes the principal invention to be claimed herein.

Referring in detail to Fig. 2,1 the two'wires of the telephone line H, H, extending from the secondary of the transformer ,5 in Fig.- l; are connected to two'tap-points l2, l3-on the primary 14 of a carriei current frequency transformer. The secondary winding l of this transformer has one terminal connected to the anode of an oscillation generator [6, which is preferably of the tetrode type now well known operator or may be operated by some form of program device which such an operator puts in motion. The negative terminal of the source H is likewise connected to one terminal of the secondary 22 of a carrier current frequency transformer, the other terminal of said secondary being connected through a current-limiting resistor to the grid of a receiver tube 23. The transformer secondary 22 is preferably shunted by a tuning condenser 24. The cathode of the receiving tube 23 is connected to a variable tap on the voltage divider I8. The anode of the receiver tube 23 is connected through a receiver relay 25 adapted to operate the, supervisory control apparatus 1 and preferably bypassed by a condenser 26. The control grid 28 of the tetrode i6 is connected through a suitable grid resistor 29 with a variable; tap 3! on the transformer secondary 22.

A primary winding 32, cooperating with the secondary winding 22 above mentioned, has one terminal connected through a tuning condenser 33 to the tap point l3 on the primary winding 14,, and has its other terminal connected to the hinge terminal of a double-throw single-pole switch. One end terminal 34 of the doublethrow switch is connected to a second tap-point on the primary winding l4 above mentioned, while the other end terminal 35 of the doublethrow switch is connected to still another tappoint on the primary E4. The double-throw switch is biased so that, in its normal or restposition, its intermediate terminal is connected to its end contact 34 and is disconnected from its end contact 35.

It will be observed that when the keying element 2| is open-circuited, no current can flow from the cathode of the tetrode I6 and the latter is accordingly deenergized. On the other hand, the receiver tube 23 has voltage impressed both on its grid, its cathode and its anode by the source I1 so that it is in an energized condition. Since the double-throw switch normally has its contact 34 in closed-circuit position, any signal transmitted through the transformer line from the telephone line I is impressed through the transformer 32, 22 upon the grid of the receiving tube 23 and is able to so energize the tube 23 as to actuate the relay 25. However, the tuning condensersv 33 and 24, respectively, tune the primary and secondary circuits, of the transformer 32, 22 so that only signals of a predetermined frequency pass sufiicient energy to the tube 23 to actuate the receiver relay. However, signals will not, in general, be impressed from the telephone line I upon the transformer 5 while all of the stations'2, 3 and 4 have their double-throw switches positioned in the normal position described above.

In order to energize the receiver tube and receiver relays in any one of the stations, it is necessary for an attendant to manually move the double-throw switch at one station to open its contacts 34 and close its contacts 35. When this is done, it will be seen that the transformer secondary l5, which is inductively coupled to the transformer winding I4, furnishes a path for flow of feedback energy through the contacts 35 of the double-throw switch and through the windings 32, 22 of the other transformer to the control grid 28 of the tetrode It. When the at tendant now closes the keying contacts 21, the tetrode I6 is energized and, by reason of the feedback circuit just mentioned, generates oscillation of a frequency determined in a well known manner by the tuning of the condensers 33, 24 and inductances of the windings 32, 22. The windings l5, l4 furthermore impress the oscillations occuring in the anode circuit of the tetrode l6 upon the line wires I l, I I and thence through the associated transformer 5 upon the line I By manipulating the keying contact 2!, the operator at the station just described can send out over the line I any series of code signals he may desire, such signals constituting a series of dots and dashes or other modulation of the carrier frequency currents generated by the tetrode 16 at the station from which he is operating.

The modulated carrier signals are thus transmitted over the line I and impressed. through their closed contacts 34 by each of the other stations on the receiver tubes 23 and their receiver relays. In ways well known in the art, the code signals may be made such that, if desired, the receiver relay at one particular receiving station will actuate the supervisory control equipment there, while the supervisory control equipment atother stations will not be set in motion by that particular code of signals.

The tap point 12 may be positioned on the winding 14 so as to match the impedance of the input circuit to tube 23 to that of the line I l. The tap point on winding [4 to which contact 35 is connected may be positioned so as to provide the amount of feedback between the plate circuit of tube I8 and its gride 28 circuit which will cause tubelii to efficiently generate oscillations of the power desired for effective transmission.

It Will be observed that the network 32, 33, 22, 24, above described, constitutes a band-pass filter of the general characteristics shown in Fig. 3, in which abscissae represent frequency and ordinates represent output voltage of the filter. This filter has the extremely desirable propertie of high transparency to signals over the frequency towhich the circuit 32, 33 is resonant (the network 22, 24 being preferably resonated to this same frequency), and is to a high degree opaque to other frequencies including the harmonics of the above-mentioned resonating frequency. I have found by numerous tests that the network of capacities and inductances just described acts very effectively to make the receiver tube sensitive only to frequencies Within a fairly narrow band; and that it further results inthe tetrode l6 oscillatin'g to produce a sine wave output voltage of great purity and freedom from harmonics. I have further found. that with the arrangement of circuits above described, the initiation of signal transmission by one station is substantially not interfered with if, before such transmitting operation of the first station ceases, an operator close-circuits the contact 35 of the double-throw switch on a second station. If, as is usually the case, the transmitters at the various stations are tuned to resonate at the same frequency, the above-described circuit connections seem to have I the result of synchronizing the phase of the voltage generated at a second incoming station with that already being impressed by a first station on the line, and of tending to maintain the voltages generated by the tetrodes H3 at different stations exactly in synchronism with each other as long as a plurality of them is simultaneously energized.

While I have described my transmitter-receiver circuit as being applied to carrier-current signalling over line wires, it will be obvious that it is of general application to currents of all frequencies and to radio transmission, as Well as to wire line transmission. The principles of my invention have been illustrated by this specific example, but it will be recognized by those skilled in the art that they are of broader application.

I claim as my invention:

1. A combination transmitter and receiver for alternating currents comprising a pair of tubes each having a main electrode circuit and a control electrode circuit, the main electrode circuit of one tube embodying a load, the main electrode circuit of the other tube embodying the primary of a transformer, thesecondary of said transformer having a plurality of tap-points, one pair of said tap-points being connected across a transmission channel, a second transformer having a primary winding connected through a tuning condenser between a tap-point on said secondary winding and the common terminal of a doublethrow switch, the outside terminal of said double-throw switch being connected respectively to two other tap-points on said secondary winding, a secondary winding on said second transformer, a tuning condenser in circuit therewith, and a connection between the control electrodes of each of said tubes and the last-mentioned secondary winding.

2. A combination transmitter and receiver for alternating currents comprising a pair of tubes each having a main electrode circuit and a control electrode circuit, the main electrode circuit of one tube embodying a load, the main electrode circuit of the other tube embodying the primary of a transformer, the secondary of said transformer having a plurality of tap-points, one pair of said tap-points being connected across a transmission channel, a second transformer having a primary winding connected through a tuning condenser between a tap-point on said secondary winding and the common terminal of a doublethrow switch, the outside terminals of said double-throw switch being connected respectively to two other tap-points on said secondary winding, a secondary winding on said second transformer, a tuning condenser in circuit therewith, a connection between the control electrodes of each of said tubes and the last-mentioned secondary winding, and keying means to impress code signals in the main electrode circuit of the secondmentioned tube. V

MYRON J. BROWN. 

